Generally, to the pipeline for water supply and hot water supply, valves, tube couplings, strainers, or other such plumbing hardware are connected. Most of these items of plumbing hardware are made of copper alloys, such as bronze and brass, which excel in castability, machinability and economy.
Particularly, the valves and couplings made of bronze and brass use these alloys in a form having lead (Pb) added thereto in prescribed amounts with a view to enhancing castability and machinability in the case of bronze and cuttableness and hot forgeability in the case of brass.
When the fluid, such as the tap water, is supplied to the valve which is made of bronze or brass containing lead, it is inferred that the part of lead of the lead-containing metal precipitated to the surface layer of the part of the valve exposed to the fluid is eluted into the tap water.
Heretofore, the tap water used for drinking has been required to conform to the standard of water quality regarding elution of lead that is examined and rated by a specific method.
Since lead is a harmful substance to the human body, the amount of its elution must be decreased to the fullest possible extent. Recently, the regulation regarding the standard of water quality with respect to the elution of lead from the plumbing hardware, such as a valve, has been directed toward further rigidification.
In the circumstance, the development of plumbing hardware, such as a valve, that satisfies the requirement has been yearned for. Thus, various methods for precluding the elution of lead as by the treatment of acid pickling or the treatment of alkali pickling have been proposed.
As a means to preclude the elution of lead by the treatment of acid-pickling which has been reduced to practice, a technique which, as disclosed in Japanese Patent No. 3345569, comprises rinsing at least the liquid-contacting part of plumbing hardware made of a lead-containing copper alloy with a cleaning fluid composed of nitric acid and hydrochloric acid incorporated additionally as an inhibitor and consequently causing the hydrochloric acid to form a coat on the surface of the liquid-contacting part and deleading the surface layer of the liquid-contacting part has been known, for example.
Then, as a means to preclude the elution of lead by the treatment of alkali pickling which has been reduced to practice, a technique which, as disclosed in the Japanese Patent No. 3182765, comprises immersing a lead-containing copper alloy in an alkaline etching liquid incorporating additionally an oxidizing agent therein, thereby selectively dissolving and removing the lead on the surface of the lead-containing copper alloy material has been known, for example.
The method of Japanese Patent No. 3182765, however, entails the problem of incurring loss of thermal energy during the treatment because the series of steps of treatment entail frequent changes of temperature.
The Japanese Patent No. 3182765 further discloses a technique that comprises continuously plating the outer surface of a lead-containing copper alloy material while giving the inner surface thereof a treatment for allaying the elution of lead at the same time.
Items of plumbing hardware, such as a valve, a tube coupling and a water tap, undergo various plating treatments including nickel plating with the object of having the appearance of the outer surface, the resistance to corrosion and the wear resistance thereof improved. When the fluid, such as the tap water, is supplied to the plumbing hardware, it will have the possibility of inducing the plumbing hardware to elute the nickel component. This nickel, on entering the human body, entails the problem of inducing diseases, such as allergy, though it has low oral toxicity because it is hardly absorbed in the intestine. Thus, the desirability of developing plumbing hardware that satisfies the upper limit of tolerance of nickel elution (0.02 mg/l or 0.01 mg/l) proposed in the amendment to the WHO drinking water guideline or in the guideline on the items of management being studied by Ministry of Welfare and Labor has been finding growing recognition.
Further, the desirability of perfecting a technique which, by realizing efficient reclamation of the varying fluid used in the treatment for precluding lead elution instead of directly discarding it as a waste liquor, permits a generous cut of cost and ensures due observance of the influence on the environment has been finding enthusiastic approval.
This invention has been perfected as a result of a diligent study performed in due respect of the true state of affairs mentioned above. This invention is aimed at providing a technique which greatly decreases the amount of lead elution as compared with the conventional standard in the use of the plumbing hardware which is made of a lead-containing metal, and further, in the plumbing hardware having a surface plated with nickel, precludes elution of the nickel by infallibly removing the nickel adhering to the inner surface of the plumbing hardware, further realizes a treatment for efficient (treating temperature, treating duration, etc.) preclusion of both or either of lead and nickel, and performs a neutralizing treatment on the varying fluid used in the treatment for precluding elution, thereby rendering the fluid usable as industrial water, permitting a generous cut in cost and allowing thorough observance of the influence on the environment.